The present invention relates generally to medical devices, and more particularly to an apparatus and method for using an ultrasonic medical device operating in a transverse mode to remove occlusions from a blood vessel. The invention also relates to an apparatus and method of using balloon catheters emitting ultrasonic energy in transverse mode, to remove vascular occlusions.
Vascular occlusions (clots or thrombi and occlusional deposits, such as calcium, fatty deposits, or plaque), result in the restriction or blockage of blood flow in the vessels in which they occur. Occlusions result in oxygen deprivation (xe2x80x9cischemiaxe2x80x9d) of tissues supplied by these blood vessels. Prolonged ischemia results in permanent damage of tissues which can lead to myocardial infarction, stroke, or death. Targets for occlusion include coronary arteries, peripheral arteries and other blood vessels. The disruption of an occlusion or thrombolysis can be effected by pharmacological agents and/or or mechanical means. However, many thrombolytic drugs are associated with side effects such as severe bleeding which can result in cerebral hemorrhage. Mechanical methods of thrombolysis include balloon angioplasty, which can result in ruptures in a blood vessel, and is generally limited to larger blood vessels. Scarring of vessels is common, which may lead to the formation of a secondary occlusion (a process known as restenosis). Another common problem is secondary vasoconstriction (classic recoil), a process by which spasms or abrupt closure of the vessel occurs. These problems are common in treatments employing interventional devices. In traditional angioplasty, for instance, a balloon catheter is inserted into the occlusion, and through the application of hydraulic forces in the range of ten to fourteen atmospheres of pressure, the balloon is inflated. The non-compressible balloon applies this significant force to compress and flatten the occlusion, thereby opening the vessel for blood flow. However, these extreme forces result in the application of extreme stresses to the vessel, potentially rupturing the vessel, or weaking it thereby increasing the chance of post-operative aneurysm, or creating vasoconstrictive or restenotic conditions. In addition, the particulate matter isn""t removed, rather it is just compressed. Other mechanical devices that drill through and attempt to remove an occlusion have also been used, and create the same danger of physical damage to blood vessels.
Ultrasonic probes are devices which use ultrasonic energy to fragment body tissue (see, e.g., U.S. Pat. No. 5,112,300; U.S. Pat. No. 5,180,363; U.S. Pat. No. 4,989,583; U.S. Pat. No. 4,931,047; U.S. Pat. No. 4,922,902; and U.S. Pat. No. 3,805,787) and have been used in many surgical procedures. The use of ultrasonic energy has been proposed both to mechanically disrupt clots, and to enhance the intravascular delivery of drugs to clot formations (see, e.g., U.S. Pat. No. 5,725,494; U.S. Pat. No. 5,728,062; and U.S. Pat. No. 5,735,811). Ultrasonic devices used for vascular treatments typically comprise an extracorporeal transducer coupled to a solid metal wire which is then threaded through the blood vessel and placed in contact with the occlusion (see, e.g., U.S. Pat. No. 5,269,297). In some cases, the transducer is delivered to the site of the clot, the transducer comprising a bendable plate (see, U.S. Pat. No. 5,931,805).
The ultrasonic energy produced by an ultrasonic probe is in the form of very intense, high frequency sound vibrations which result in powerful chemical and physical reactions in the water molecules within a body tissue or surrounding fluids in proximity to the probe. These reactions ultimately result in a process called xe2x80x9ccavitation,xe2x80x9d which can be thought of as a form of cold (i.e., non-thermal) boiling of the water in the body tissue, such that microscopic bubbles are rapidly created and destroyed in the water creating cavities in their wake. As surrounding water molecules rush in to fill the cavity created by collapsed bubbles, they collide with each other with great force. This process is called cavitation and results in shock waves running outward from the collapsed bubbles which can wear away or destroy material such as surrounding tissue in the vicinity of the probe.
Some ultrasonic probes include a mechanism for irrigating an area where the ultrasonic treatment is being performed (e.g., a body cavity or lumen) to wash tissue debris from the area. Mechanisms used for irrigation or aspiration described in the art are generally structured such that they increase the overall cross-sectional profile of the probe, by including inner and outer concentric lumens within the probe to provide irrigation and aspiration channels. In addition to making the probe more invasive, prior art probes also maintain a strict orientation of the aspiration and the irrigation mechanism, such that the inner and outer lumens for irrigation and aspiration remain in a fixed position relative to one another, which is generally closely adjacent the area of treatment. Thus, the irrigation lumen does not extend beyond the suction lumen (i.e., there is no movement of the lumens relative to one another) and any aspiration is limited to picking up fluid and/or tissue remnants within the defined distance between the two lumens.
Another drawback of existing ultrasonic medical probes is that they typically remove tissue slowly in comparison to instruments which excise tissue by mechanical cutting. Part of the reason for this is that most existing ultrasonic devices rely on a longitudinal vibration of the tip of the probe for their tissue-disrupting effects. Because the tip of the probe is vibrated in a direction in line with the longitudinal axis of the probe, a tissue-destroying effect is only generated at the tip of the probe. One solution that has been proposed is to vibrate the tip of the probe in a transverse directionxe2x80x94i.e. perpendicular to the longitudinal axis of the probe,xe2x80x94in addition to vibrating the tip in the longitudinal direction. For example, U.S. Pat. No. 4,961,424 to Kubota, et al. discloses an ultrasonic treatment device which produces both a longitudinal and transverse motion at the tip of the probe. The Kubota, et al. device, however, still relies solely on the tip of the probe to act as a working surface. Thus, while destruction of tissue in proximity to the tip of the probe is more efficient, tissue destruction is still predominantly limited to the area in the immediate vicinity at the tip of the probe. U.S. Pat. No. 4,504,264 to Kelman discloses an ultrasonic treatment device which improves the speed of ultrasonic tissue removal by oscillating the tip of the probe in addition to relying on longitudinal vibrations. Although tissue destruction at the tip of the device is more efficient, the tissue destroying effect of the probe is still limited to the tip of the probe.
There is a need in the art for improved devices, systems, and methods, for treating vascular diseases, particularly stenotic diseases which occlude the coronary and other arteries. In particular, there is a need for methods and devices for enhancing the performance of angioplasty procedures, where the ability to introduce an angioplasty catheter through a wholly or partly obstructed blood vessel lumen can be improved. There is also a need for mechanisms and methods that decrease the likelihood of subsequent clot formation and restenosis.
The invention is directed to a method and an apparatus for removing occlusions in a blood vessel. The invention has particular application in removal of occlusions in saphenous vein grafts used in coronary bypass procedures, restoring these grafts to patency without damaging anastomosing blood vessels. The method according to the invention comprises inserting a probe member comprising a longitudinal axis into a vessel, positioning the member in proximity to the occlusion, and providing ultrasonic energy to the member. The device is designed to have a small cross-sectional profile, which also allows the probe to flex along its length, thereby allowing it to be used in a minimally-invasive manner. The probe, because it vibrates transversely, generates a plurality of cavitation nodes along the longitudinal axis of the member, thereby efficiently destroying the occlusion. A significant feature of the invention is the retrograde movement of debris, e.g., away from the tip of the probe, resulting from the transversely generated energy. Probes of the present invention are described in the Applicant""s co-pending provisional applications U.S. Ser. Nos. 60/178,901 and 60/225,060 which further describe the design parameters for an ultrasonic probe operating in a transverse mode and the use of such a probe to remodel tissues. The entirety of these applications are herein incorporated by reference.
In one aspect, the invention relates to one or more sheaths which can be adapted to the probe tip, thereby providing a means of containing, focussing, and transmitting energy generated along the length of the probe to one or more defined locations. Sheaths for use with an ultrasonic medical device are described in the Applicant""s co-pending utility application U.S. Ser. No. 09/618,352, the entirety of which is hereby incorporated by reference. The sheaths of the present invention also provide the user with a means of protecting regions of tissue from physical contact with the probe tip. In one embodiment of the invention the sheaths also comprise a means for aspiration and irrigation of the region of probe activity. In another embodiment of the invention, a plurality of sheaths are used in combination to provide another level of precision control over the direction of cavitation energy to a tissue in the vicinity of the probe. In one embodiment of the invention, the sheath encloses a means of introducing fluid into the site of the procedure, and a means for aspirating fluid and tissue debris from the site of the procedure. In a further embodiment, the probe tip can be moved within the sheath. In yet another embodiment, the irrigation and aspiration means, and the probe tip, can all be manipulated and repositioned relative to one another within the sheath. In another embodiment, the sheath is shaped in such a way that it may capture or grasp sections of tissue which can be ablated with the probe. In yet another embodiment, the sheath provides a guide for the probe tip, protecting tissues from accidental puncture by the sharp, narrow diameter tip, or from destruction by energy emitted radially from the probe during introduction of the probe to the site. The sheath may be applied to the probe tip prior to insertion of the probe into the patient, or the sheath can be inserted into the patient prior to the insertion of the probe. The sheath of the present invention can be used to fix the location of one or more shapes relative to the nodes or anti-nodes of a probe acting in transverse action. The location of the reflective shapes can amplify the acoustical wave thereby magnifying the energy. This allows for the use of very small diameter probes which themselves would not have the requisite structural integrity to apply and translate acoustical energy into sufficient mechanical energy to enable ablation of tissues. The reflective shapes can also focus or redirect the energy, effectively converting a transverse probe emitting cavitation energy along its length, to a directed, side fire ultrasonic device.
In another embodiment, the probe, which may or may not contain a probe sheath, is used in conjunction with an expandable balloon dilatation catheter, providing a means of resolving the occlusion without imparting stress, or inflicting stress injury to a vessel. The balloon catheter acts as a carrier means for guiding the probe wire to the desired site, and acts as a means to position the wire within the lumen of the vessel. With the balloon inserted within the confines of an occlusion, inflation of the balloon provides a means of continuous contact with the potentially irregularly shaped vessel lumen. Introduction of ultrasonic energy into the balloon by the transversely vibrating probe wire thereby results in uniform communication of energy to the regions of the occluded vessel in contact with the balloon. Since the balloon is inflated to much lower pressures than in traditional balloon angioplasty procedures, neither the occlusion or the vessel is compressed, thereby eliminating the problems of stress injury to the vessel. Likewise, as the ultrasound energy fragments the occlusion, the vessel is cleared of the problematic material, rather than simply compressing it into the vessel.
In one embodiment of the invention, a light transmitting element in inserted into the blood vessel along with, or after, the probe (with or without probe sheath) and balloon catheter. The light transmitting element is transmits optical data about the occlusion. In another embodiment of the invention, the probe/sheath and balloon catheter is used with such medical devices, such as a stent, stent graft, trocar, or other such intravascular devices. The invention is particularly useful in clearing occlusions within stents or other such devices where compression is undesirable or not warranted.
In another aspect of the invention, the probe, with or without a probe sheath, and with or without the balloon catheter, may be provided in a sharps container, in the form of a kit. A sharps container of the present invention is the subject of the Applicant""s co-pending utility application U.S. Ser. No. 09/775,908, the entirety of which is hereby incorporated by reference. In yet another embodiment, the kit provides instructions, for example, instructions for assembling and tuning the probe, and the appropriate frequency range for the medical procedure. The kit may further comprise packaging whereby the probe, sheath, and balloon catheter are pre-sterilized, and sealed against environmental contaminants. In another embodiment, the container complies with regulations governing the storage, handling, and disposal of sharp medical devices, and used medical devices such as a sheath or balloon catheter.